JP2011221400A - Liquid crystal display and method for manufacturing liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display capable of improving transmittance, while maintaining excellent voltage response characteristics.SOLUTION: A pixel electrode 12 has a first sub electrode 12A, a dielectric layer 13, and a second sub electrode 12B in order from a liquid crystal layer 15 side in a liquid crystal display 1. A magnitude relation between an applied voltage to an area A right above a slit in a liquid crystal layer 15 and an applied voltage to an area B without the slit in the liquid crystal layer 15 may be controllable according to a purpose by optionally setting electric potentials Va and Vb supplied to the first sub electrode 12A and the second sub electrode 12B, respectively. Driving is carried out to reduce an electric field distortion in the whole liquid crystal layer 15 when displaying an image to suppress a decrease in local transmittance due to the slit position. In a manufacturing process (pretilt imparting process), electric field distortion (lateral electric field) favorable to imparting a pretilt is generated.

Description

  The present invention relates to a liquid crystal display device using, for example, a VA mode liquid crystal and a method for manufacturing the same.

  2. Description of the Related Art In recent years, for example, VA (Vertical Alignment) mode liquid crystal is used in a liquid crystal display (LCD). In such a liquid crystal display device, a liquid crystal layer is sealed through a vertical alignment film between a substrate having a pixel electrode and a substrate having a counter electrode. This liquid crystal layer has a negative dielectric anisotropy. That is, it has the property that the dielectric constant of the liquid crystal molecules is smaller in the major axis direction than in the minor axis direction. With such a structure, the liquid crystal is aligned along the direction in which the major axis direction of the liquid crystal molecules is perpendicular to the substrate surface when no voltage is applied (OFF state), but when the voltage is applied (ON state). Is an orientation in which the liquid crystal molecules are tilted (tilted) in accordance with the magnitude of the voltage.

  However, when a voltage is applied to the liquid crystal layer when no voltage is applied, the liquid crystal molecules aligned perpendicular to the substrate surface fall down, but the direction of the fall is arbitrary. As a result, the alignment of the liquid crystal molecules is disturbed and the response to the voltage is delayed, or the desired transmittance is hardly obtained.

  Therefore, in order to regulate the direction in which the liquid crystal molecules fall during voltage response, a technique is used in which the liquid crystal molecules are pre-tilted in a specific direction (so-called pretilt is provided). That is, for example, a rubbing method in which an alignment film is rubbed with a cloth or the like to form grooves along a certain direction, an MVA (Multi-domain Vertical Alignment) method in which electrodes are provided with slits or ribs (projections) at a predetermined interval, PVA (Patterned Vertical Alignment) method. In addition, a HAN type (hybrid alignment type) has been proposed in which one substrate side is vertically aligned and the other substrate side is horizontally aligned (for example, Patent Document 1).

  More recently, a PSA (Polymer Sustained Alignment) system in which a plurality of slits are provided in the pixel electrode, the counter electrode is solid (no slit), and liquid crystal molecules are held in a pretilt state by a polymer has been proposed (Patent Document). 2). According to such a method using pretilt, the response characteristics of the liquid crystal molecules to the voltage can be improved.

JP 2003-202575 A US Pat. No. 7,145,622

  However, although the voltage response characteristic can be improved by the method of Patent Document 2, the portion corresponding to the slit of the pixel electrode (immediately above the slit) in the liquid crystal layer is the other portion (the portion having no slit). It is difficult to apply a sufficient voltage compared to. In addition, since electric field distortion (lateral electric field) occurs particularly near the edge of the slit, the liquid crystal is aligned while being twisted. For this reason, at the time of driving, there is a problem that a dark line (a portion where the amount of light transmission is locally small) is generated corresponding to the slit position and it is difficult to obtain high transmittance.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a liquid crystal display device and a method for manufacturing the liquid crystal display device that can improve the transmittance while maintaining good voltage response characteristics. There is.

  A liquid crystal display device according to the present invention includes a liquid crystal layer, a pair of substrates opposed to each other with the liquid crystal layer interposed therebetween, a plurality of pixel electrodes provided on the liquid crystal layer side of one of the pair of substrates, And a counter electrode provided on the other substrate so as to face the pixel electrode. Each pixel electrode, in order from the liquid crystal layer side, a first sub-electrode having one or a plurality of slits, a dielectric layer, and at least a second sub-electrode disposed in a region facing the slit of the first sub-electrode. And a sub-electrode.

  The method for manufacturing a liquid crystal display device according to the present invention includes a step of forming a plurality of pixel electrodes on one of a pair of substrates, a step of forming a counter electrode on the other substrate, and a liquid crystal layer between the pair of substrates. And a step of applying a pretilt to the liquid crystal layer by exposing the liquid crystal layer while applying a voltage to the liquid crystal layer through the pixel electrode and the counter electrode. In the step of forming a plurality of pixel electrodes, each pixel electrode includes a second sub-electrode, a dielectric layer, and a first slit having one or a plurality of slits facing the second sub-electrode from one substrate side. The sub-electrodes are formed in this order.

  In the liquid crystal display device and the manufacturing method of the liquid crystal display device of the present invention, the pixel electrode has a two-layer electrode structure including a first sub-electrode having a slit and at least a second sub-electrode disposed to face the slit. In addition, a dielectric layer is provided between the first and second sub-electrodes. For this reason, for example, by appropriately setting the supply potential to each electrode, the magnitude relationship between the voltage applied to the region immediately above the slit in the liquid crystal layer and the voltage applied to the region without the slit can be freely controlled. It becomes. Accordingly, when displaying an image, it is possible to drive the entire liquid crystal layer so as to reduce the electric field distortion. As a result, a local decrease in transmittance due to, for example, the slit position is suppressed. On the other hand, in the manufacturing process, it is possible to generate electric field distortion (lateral electric field) advantageous for pretilt application.

  Specifically, at the time of video display (in a liquid crystal display device), it is desirable that the drive unit supplies the following potential to each pixel electrode and the counter electrode, for example. That is, the voltage applied to the first region immediately above the slit of the liquid crystal layer (voltage corresponding to the potential difference between the first sub-electrode and the counter electrode) and the voltage applied to the second region without the slit (second sub-electrode) It is preferable to supply the potential so that the difference is more preferably equal so that the difference between the voltage and the voltage corresponding to the potential difference between the counter electrode and the counter electrode is reduced.

  On the other hand, in the manufacturing process (in the manufacturing method of the liquid crystal display device), it is desirable to apply, for example, the following voltage to the liquid crystal layer in the pretilt providing step. That is, the voltage applied to the first region immediately above the slit (voltage corresponding to the potential difference between the first sub-electrode and the counter electrode) and the voltage applied to the second region without the slit (second sub-electrode and counter electrode) The voltage according to the potential difference between the first and second potentials is preferably different from each other.

  According to the liquid crystal display device and the method of manufacturing the same of the present invention, the pixel electrode includes the first sub-electrode having a slit, the dielectric layer, and at least the second sub-electrode facing the slit. The electric field distribution in the layer can be controlled according to the purpose. For example, during image display, electric field distortion is suppressed to suppress local reduction in transmittance, while in the manufacturing process, pretilt can be efficiently applied by generating electric field distortion. Therefore, it is possible to improve the transmittance while maintaining good voltage response characteristics.

1 is a block diagram illustrating an overall configuration of a liquid crystal display device according to an embodiment of the present invention. It is sectional drawing of the partial area | region of the pixel shown in FIG. It is a schematic diagram for demonstrating the pretilt angle of a liquid crystal molecule. FIG. 3 is a plan view of a first sub electrode and a second sub electrode shown in FIG. 2. FIG. 3 is a schematic cross-sectional view for explaining an outline of potential supply to the pixel electrode and the counter electrode shown in FIG. 2. FIG. 6 is a circuit configuration diagram between a pixel electrode and a counter electrode illustrated in FIG. 5. It is a cross-sectional schematic diagram for demonstrating the manufacturing method (pretilt addition process) of the liquid crystal display device shown in FIG. FIG. 3 is a characteristic diagram illustrating an electric field distribution (equipotential distribution) of Example 1. FIG. 3 is a characteristic diagram illustrating an electric field distribution (equipotential distribution) of Example 1. It is sectional drawing of the one part area | region of the pixel in the liquid crystal display device which concerns on a comparative example. It is the characteristic view showing the electric field distribution (equipotential distribution) of the comparative example, and the plane schematic diagram showing the orientation state of a liquid crystal molecule. FIG. 10 is a characteristic diagram illustrating a relationship (T = 200 nm) between a supply potential to a second sub electrode and transmittance in Example 2. FIG. 10 is a characteristic diagram illustrating a relationship (T = 400 nm) between a supply potential to a second sub electrode and transmittance in Example 2. FIG. 6 is a characteristic diagram illustrating a relationship (T = 1000 nm) between a supply potential to a second sub electrode and transmittance in Example 2. FIG. 6 is a characteristic diagram showing an electric field distribution (equipotential distribution) of Example 3. 6 is a plan view showing a measurement result of transmittance distribution of Example 3. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The description will be given in the following order.

Embodiment (Example in which a pixel electrode has a laminated structure in which a dielectric film is sandwiched between two electrodes)
1. 1. Configuration of liquid crystal display device Manufacturing method of liquid crystal display device (setting example of potentials Va and Vb when pretilt is applied)
3. Operation of liquid crystal display device (setting example of potentials Va and Vb during video display)

<Embodiment>
[Configuration of Liquid Crystal Display Device 1]
FIG. 1 shows an overall configuration of a liquid crystal display device (liquid crystal display device 1) according to an embodiment of the present invention. The liquid crystal display device 1 includes, for example, a liquid crystal display panel 2, a backlight 3, a data driver 51, a gate driver 52, a timing control unit 61, and a backlight driving unit 62, and performs video display based on an external input signal Din. is there.

  The backlight 3 is a light source that emits light toward the liquid crystal display panel 2, and is disposed on the back surface (surface on the incident side polarizing plate 19 side described later) side of the liquid crystal display panel 2. The backlight 3 includes, for example, an LED (Light Emitting Diode) and a CCFL (Cold Cathode Fluorescent Lamp). The backlight drive unit 62 controls the lighting operation (light emission operation) of the backlight 3.

  The timing control unit 61 controls driving timings of the gate driver 52, the data driver 51, and the backlight driving unit 62, and supplies a video signal based on the external input signal Din to the data driver 51.

  The gate driver 52 drives each pixel 10 in the liquid crystal display panel 2 according to timing control by the timing control unit 61. The data driver 51 performs D / A conversion on the video signal supplied from the timing control unit 61 (video signal based on the external input signal Din) and converts the D / A converted video signal to the liquid crystal display panel 2. Are output to each pixel 10. Potentials Va and Vb (details will be described later) set in accordance with the video signal are supplied to the pixels 10 selected by the drive signals from the gate driver 52 and the data driver 51, respectively.

  The liquid crystal display panel 2 modulates the light emitted from the backlight 3 based on the drive signal supplied from the gate driver 52 and the video signal supplied from the data driver 51. The liquid crystal display panel 2 includes a plurality of pixels 10 arranged in a matrix as a whole.

  FIG. 2 shows a cross-sectional configuration of the liquid crystal display panel 2. However, FIG. 2 shows only a partial region of the pixel 10. The liquid crystal display panel 2 has a liquid crystal layer 15 sandwiched between a drive substrate 11 and a counter substrate 18. An incident side polarizing plate 19 and an output side polarizing plate 20 are disposed outside the drive substrate 11 and the counter substrate 18. Are pasted together. A pixel electrode 12 is provided for each pixel on the surface of the driving substrate 11 on the liquid crystal layer 15 side, and an alignment film 14 is formed so as to cover the surface of the pixel electrode 12. On the surface of the counter substrate 18 on the liquid crystal layer 15 side, a counter electrode 17 is disposed over almost the entire effective display area, and an alignment film 16 is formed to cover the surface of the counter electrode 17.

  The drive substrate 11 is, for example, a drive circuit for driving the pixels 10 on a glass substrate, for example, the gate driver 52, the data driver 51, the timing control unit 61, the backlight control unit 62, and the like described above are disposed. . On the drive substrate 11, each pixel electrode 12 has a gate line, a source line, or the like for transmitting drive signals from the gate driver 52 and the data driver 51, and a TFT (thin film transistor) (not shown). ) Etc. are connected. One or two TFTs are provided for each pixel 10. Although details will be described later, in the present embodiment, the pixel electrode 12 has two electrode layers, a first sub-electrode 12A and a second sub-electrode 12B. Therefore, when supplying the same potential to the first sub electrode 12A and the second sub electrode 12B, the number of TFTs is one. When different potentials are supplied to the first sub electrode 12A and the second sub electrode 12B, TFTs and wirings are separately provided on the first sub electrode 12A and the second sub electrode 12B.

  The counter substrate 18 is formed by arranging, for example, red (R), green (G), and blue (B) filters on the surface of the glass substrate (the surface on the counter electrode 17 side or the surface on the output side polarizing plate 20 side). It has a color filter (not shown).

  The counter electrode 17 is made of, for example, a transparent conductive film such as ITO, and is provided as an electrode common to each pixel 10 (opposing all the pixel electrodes 12). The counter electrode 17 is held at a predetermined potential, for example, a ground potential.

  The alignment films 14 and 16 are, for example, vertical alignment films, and the liquid crystal molecules in the liquid crystal layer 15 (specifically, liquid crystal molecules in the vicinity of the alignment films 14 and 16) have their major axis direction (director) with respect to the substrate surface. It is oriented so as to be almost vertical. As such alignment films 14 and 16, for example, a vertical alignment agent such as polyimide or polysiloxane is used.

  The liquid crystal layer 15 includes, for example, vertical alignment type liquid crystal molecules. In the liquid crystal layer 15, the liquid crystal molecules have a rotationally symmetric shape with the major axis and the minor axis as central axes, for example, and have negative dielectric anisotropy (the property that the dielectric constant in the major axis direction is smaller than that in the minor axis direction). ).

  In the liquid crystal layer 15, as shown in FIG. 3, liquid crystal molecules (liquid crystal molecules 15 a) in the vicinity of the interface with the alignment films 14 and 16 have a major axis direction D 1 on the substrate surface due to the restriction from the alignment films 14 and 16. While being oriented so as to be substantially vertical, it is held in a state slightly tilted from the vertical direction. That is, a so-called pretilt is given in the vicinity of the interface between the liquid crystal layer 15 and the alignment films 14 and 16, and the tilt angle (pretilt angle) θ of the liquid crystal molecules 15a from the vertical direction is, for example, about 0 ° to 3 °. is there. Such a pretilt is held by the polymer in the vicinity of the interface between the liquid crystal layer 15 and the alignment films 14 and 16, and other liquid crystal molecules (for example, in the thickness direction of the liquid crystal layer 15) follow the alignment of the liquid crystal molecules in the vicinity of the interface. The liquid crystal molecules in the vicinity of the center in FIG.

  The incident-side polarizing plate 19 and the outgoing-side polarizing plate 20 are arranged, for example, in a crossed Nicols state, and light from the backlight 3 is blocked in a voltage non-application state (off state) and a voltage application state (on state). Then, it is made to transmit. That is, the incident side polarizing plate 19 and the outgoing side polarizing plate 20 are bonded to the drive substrate 11 and the counter substrate 18 so as to be normally black.

(Configuration of pixel electrode 12)
The pixel electrode 12 is formed by laminating a second sub electrode 12B, a dielectric layer 13, and a first sub electrode 12A in order from the drive substrate 11 side.

  FIG. 4A schematically shows a planar configuration of the first sub electrode 12A. The first sub-electrode 12A is provided with a plurality of linear slits 12a1 in a predetermined pattern. For example, the slit 12a1 is provided so as to extend along a plurality of directions (here, four directions A1 to A4) in the electrode surface. By having such a slit pattern, regions having different alignment directions are formed (alignment division) in the pixel 10, so that viewing angle characteristics are improved. The first sub-electrode 12A is made of a transparent conductive film such as ITO (indium tin oxide), and has a thickness of 50 nm to 200 nm, for example. The width S of the slit 12a1 is 2 nm to 8 nm, for example, and the width L of the electrode portion 12a2 extending in the same direction as the slit 12a1 is 2 nm to 8 nm, for example.

  Note that the pattern of the slits 12a1 is not limited to the pattern extending along the four directions, and various patterns such as a stripe shape and a V shape can be employed. Further, the width S and the number of the slits 12a1 and the width L and the number of the electrode portions 12a2 can be arbitrarily set.

  FIG. 4B schematically shows a planar configuration of the second sub-electrode 12B. The second sub electrode 12B is provided over the entire area of the first sub electrode 12A. Here, the second sub electrode 12B is an electrode having no slit or gap. Hereinafter, the second sub electrode 12B will be described as a “solid electrode”. However, the second sub electrode 12B may be formed at least in a region facing the slit 12a1 of the first sub electrode 12A (a region immediately below the slit 12a1). That is, the second sub-electrode 12B does not necessarily have to be a solid electrode, and there are slits, gaps, and the like in the region facing the electrode portion 12a2 of the first sub-electrode 12A (the region immediately below the electrode portion 12a2). It may be provided. The second sub electrode 12B is made of a transparent conductive film such as ITO, and has a thickness of 50 nm to 200 nm, for example. 4A and 4B corresponds to the configuration of the first sub electrode 12A and the second sub electrode 12B in FIG.

  The dielectric layer 13 is inserted between the first sub electrode 12A and the second sub electrode 12B for each pixel 10 or over the entire effective display area. The dielectric layer 13 is made of, for example, an inorganic insulating film or an organic insulating film such as silicon nitride (SiN). When the dielectric constant is 3 to 7, for example, the thickness is 0.01 μm to 10 μm, which is desirable. Is 0.1 μm to 3 μm.

  As described above, the pixel electrode 12 has a two-layer electrode structure in which the first sub-electrode 12A and the second sub-electrode 12B are stacked with the dielectric layer 13 interposed therebetween. In such an electrode structure, the first sub electrode 12A closer to the liquid crystal layer 15 has a plurality of slits 12a1, and the second sub electrode 12B far from the liquid crystal layer 15 is a solid electrode.

The first sub-electrode 12A and the second sub-electrode 12B can be supplied with the same or different potential by driving the timing control unit 61, the gate driver 52, and the data driver 51, respectively. For example, as shown in FIG. 5, the potential Va can be supplied to the first sub-electrode 12A and the potential Vb can be supplied to the second sub-electrode 12B, and the counter electrode 17 is set to a ground potential, for example. . Thus, a voltage corresponding to the potential difference (Vb) between the counter electrode 17 and the second sub electrode 12B is applied to the region (region A) immediately above the slit 12a1 of the liquid crystal layer 15. On the other hand, a voltage corresponding to the potential difference (Va) between the counter electrode 17 and the first sub electrode 12A is applied to a region (region B) immediately above the electrode portion 12a2 of the liquid crystal layer 15. FIG. 6 shows a circuit configuration in the areas A and B. However, _CLC is a capacitance between the first sub electrode 12A and the counter electrode 17, and C _INS is a capacitance between the first sub electrode 12A and the second sub electrode 12B. The electrostatic capacity C _LC assumes the center part of the electrode part 12a2, and the electrostatic capacity C _INS assumes the center part of the slit 12a1.

  The potentials Va and Vb may be the same or different from each other. However, when the same potential is used, one TFT may be provided for each pixel 10 as described above. On the other hand, when the potentials Va and Vb are not limited to the same potential but can be set to different potentials, two TFTs may be provided for each pixel 10.

With such an electrode structure of the pixel electrode 12, a desired potential is supplied to each of the first sub electrode 12A and the second sub electrode 12B in accordance with each case of a manufacturing process (when pretilt is applied) and an image display described later. It has come to be.

[Method of Manufacturing Liquid Crystal Display Device 1]
(1. Panel sealing process)
The liquid crystal display device 1 can be manufactured, for example, as follows. That is, first, after forming two TFTs on the surface of the drive substrate 11 by a known thin film process, a planarizing film made of an insulating film is formed so as to cover the surface on which the TFTs are formed. On the planarizing film, the second sub electrode 12B is formed by, for example, vapor deposition or sputtering, and then patterned into a rectangular shape for each pixel 10 by photolithography. Subsequently, the dielectric layer 13 is formed on the second sub electrode 12B so as to have a desired thickness by, for example, plasma CVD. Next, after the first sub-electrode 12A is formed on the dielectric layer 13 by, for example, vapor deposition or sputtering, a plurality of slits 12a1 are patterned by photolithography. A contact hole is provided in the dielectric layer 13 and the planarizing film, and the first sub-electrode 12A and the second sub-electrode 12B are electrically connected to the TFT formed on the drive substrate 11 through the contact hole, respectively. Try to connect. A vertical alignment agent is applied so as to cover the surface of the pixel electrode 12 thus formed, specifically, the surface of the electrode portion 12a2 of the first sub-electrode 12A and the surface of the dielectric layer 13 exposed by the slit 12a1. For example, the alignment film 14 is formed by applying and baking by a spin coat method.

  On the other hand, after the counter electrode 17 is formed on the surface of the counter substrate 18 by, for example, vapor deposition or sputtering, a vertical alignment agent is applied to the surface of the counter electrode 17 by, for example, spin coating, and baked. An alignment film 16 is formed.

  Thereafter, for example, a UV curable or thermosetting seal portion is printed on the peripheral region of the drive substrate 11, and a liquid crystal mixed with, for example, a UV curable monomer is dropped into the region surrounded by the seal portion. As a result, the liquid crystal layer 15 is formed. Thereafter, the counter substrate 18 is overlaid on the drive substrate 11 via a spacer made of, for example, a photosensitive acrylic resin, and the seal portion is cured. In this manner, a panel sealing body in which the liquid crystal layer 15 is sealed between the driving substrate 11 and the counter substrate 18 is formed.

(2. Pretilt addition process)
Subsequently, in the panel sealing body formed as described above, a pretilt is added to the liquid crystal layer 15 by exposure (UV irradiation) while applying a voltage to the liquid crystal layer 15. Specifically, as shown in FIG. 7A, the potential Va is applied to the first sub-electrode 12A of the pixel electrode 12 and the potential Vb is applied to the second sub-electrode 12B while the counter electrode 17 is held at the ground potential. Supply. However, at this time, the potentials Va and Vb are set so that the voltages applied to the regions A and B are different. Specifically, the potentials Va and Vb may be set so as to satisfy the following expression (5).
Vb ≠ Va × (C _INS + C _LC ) / C _INS (5)

  As a result, electric field distortion (lateral electric field) is generated in the liquid crystal layer 15, and the liquid crystal molecules 15a are easily tilted according to the pattern of the slits 12a1. Then, UV irradiation is performed in a state where the liquid crystal molecules 15 a are tilted, whereby the monomer mixed in the liquid crystal layer 15 is cured in the vicinity of the interface with the alignment films 14 and 16. Thereafter, as shown in FIG. 7B, when the first sub-electrode 12A and the second sub-electrode 12B are set to the ground potential, and the liquid crystal layer 15 is returned to the no-voltage application state, the polymer formed in the vicinity of the interface is formed. Holds the liquid crystal molecules 15a slightly tilted from the vertical direction. In this way, the pretilt angle θ as shown in FIG. 3 is given to the liquid crystal molecules 15a.

The potentials Va and Vb may be different from each other as long as they satisfy the above expression (5), but are set to be the same as each other, that is, to satisfy the following expression (6). May be. When Expression (6) is satisfied, as described above, it is sufficient to provide one TFT for driving the first sub electrode 12A and the second sub electrode 12B, so that the device configuration is simplified.
Vb = Va (6)

  8A to 8C and FIGS. 9A and 9B, the electric field distribution (equipotential distribution) formed in the liquid crystal layer 15 by the potentials Va and Vb satisfying the above formula (5). (Example 1) about is shown. However, in each figure, X (μm) indicates a scale in a direction orthogonal to the extending direction of the slit 12a1 on the substrate surface. Z (μm) is a scale in the thickness direction of the liquid crystal layer 15, where Z = 0 is the first sub-electrode 12A side (alignment film 14 side), and Z = 3.5 μm is the counter electrode side (alignment film 16 side). To do.

In Example 1, in the panel sealing body as described above, the width S of the slit 12a1 of the first sub-electrode 12A is 4 μm, the width L of the electrode portion 12a2 is 4 μm, and the dielectric layer 13 has a dielectric constant ε = 6. And SiN having a thickness T = 200 nm was used. For the alignment films 14 and 16, a vertical alignment film (JALS2131-R6: manufactured by JSR) is applied on the first sub-electrode 12A, dried on a hot plate at 80 ° C. for 80 seconds, and then in a clean oven in a nitrogen atmosphere. And was baked at 200 ° C. for 60 minutes. As the liquid crystal layer 15, VA liquid crystal having a dielectric constant ε (⊥) = 6.2, ε (‖) = 3.0 and a thickness of 3.5 μm is used, and an acrylic monomer (A-BP-2E: manufactured by Shin-Nakamura Chemical Co., Ltd.). ) Was mixed by 0.3 wt%. Further, with such a configuration, the capacitance C _LC was 15.8 × 10 ⁻¹² F, and the capacitance C _INS was 267 × 10 ⁻¹² F (the area was converted to 1 μm ² ). The vacuum dielectric constant ε0 was 8.9 × 10 ⁻¹² F.

  For such a panel sealing body, the potential Va was set to 10 V (constant), and a voltage was applied to the liquid crystal layer 15 while changing the potential Vb. Specifically, the ratio of the potential Vb to the potential Va (Vb / Va) was set to be 0, 0.5, 0.75, 1, and 1.2, respectively. In Example 1, by setting the potentials Va and Vb so as to satisfy the above formula (5), an electric field distortion effective for providing a pretilt is generated in the liquid crystal layer 15, and the electric field is changed depending on the ratio of the potentials Va and Vb. It can be seen that the degree of distortion is different. Here, the case of Vb / Va = 0.75 shown in FIG. 8C is an ideal electric field distribution for pretilt formation. However, the combination of the potentials Va and Vb is not limited to this. The desired pretilt angle, the liquid crystal material and thickness of the liquid crystal layer 15, the monomer material, the scale of the slit 12a1 and the electrode portion 12a2 of the first sub-electrode 12A, the dielectric What is necessary is just to set suitably according to the material, thickness, etc. of the layer 13. FIG.

  As described above, the incident-side polarizing plate 19 and the output-side polarizing plate 20 are bonded to the back surface of the drive substrate 11 of the panel sealing body after the pretilt is imparted so as to have a crossed Nicols arrangement. . Thereby, the liquid crystal display device 1 shown in FIG. 1 is completed.

[Operation of the liquid crystal display device 1]
(Video display operation)
In the liquid crystal display device 1, an image is displayed by applying a driving voltage based on the external input signal Din between the pixel electrode 12 and the counter electrode 17 in the following manner. Specifically, under the control of the timing control unit 61, the gate driver 52 sequentially supplies scanning signals to the gate lines connected to the pixels 10, and the data driver 51 displays video based on the external input signal Din. A signal is supplied to a predetermined source line. As a result, the pixel 10 located at the intersection of the source line supplied with the video signal and the gate line supplied with the scanning signal is selected, and the drive voltage is applied to the pixel 10.

  In the selected pixel 10, when a driving voltage is applied, the alignment state of the liquid crystal molecules 15 a included in the liquid crystal layer 15 changes according to the potential difference between the pixel electrode 12 and the counter electrode 17. Specifically, when a driving voltage is applied from the state in which no voltage is applied, the liquid crystal molecules 15a located in the vicinity of the alignment films 14 and 16 are tilted, and the central portion in the thickness direction of the liquid crystal layer 15 so as to follow the operation. In turn, the liquid crystal molecules 15a fall down sequentially. At this time, since the pretilt angle is given to the liquid crystal molecules 15a, the liquid crystal molecules 15a are easily tilted in the tilt direction of the liquid crystal molecules 15a, so that the response time to the driving voltage is shortened. As a result, the optical characteristics of the liquid crystal layer 15 change, and the light incident on the liquid crystal display panel 2 from the backlight 3 is modulated and emitted. In the liquid crystal display device 1, an image is displayed in this way.

  Here, an image display operation of the liquid crystal display device according to the comparative example will be described. FIG. 10 illustrates a cross-sectional configuration of a partial region of a pixel of a liquid crystal display device according to a comparative example. In this liquid crystal display device, a liquid crystal layer 104 is sandwiched between a driving substrate 101 and a counter substrate 107, and an incident side polarizing plate 108 and an output side polarizing plate 109 are disposed outside the driving substrate 101 and the counter substrate 107. Are pasted together. A pixel electrode 102 is provided for each pixel on the surface of the driving substrate 101 on the liquid crystal layer 104 side, and an alignment film 103 is formed to cover the surface of the pixel electrode 102. On the surface of the counter substrate 107 on the liquid crystal layer 104 side, a counter electrode 106 is disposed over almost the entire effective display area, and an alignment film 105 is formed to cover the surface of the counter electrode 106. In other words, the liquid crystal display device of the comparative example employs a so-called fine slit structure in which the pixel electrode 103 has a plurality of slits 102a1.

  FIG. 11A schematically shows the electric field distribution during video display of the comparative example, and FIG. 11B schematically shows the alignment state of the liquid crystal molecules (liquid crystal molecules 104a) at that time. However, in FIG. 11B, Y (μm) indicates the scale in the extending direction of the slit 12a1 on the substrate surface, and the upper side of the portion surrounded by the broken line on the Y axis is the slit 102a1 of the pixel electrode 102 and the lower side. Corresponds to the electrode portion 102a2. In addition, the liquid crystal molecules 104a are schematically represented by using a circular portion and a rod-shaped portion, and the rod-shaped portion indicates the major axis direction (director) of the liquid crystal molecules, and the circular portion indicates the major axis direction tip (liquid crystal molecule). "Head"). For example, the liquid crystal molecules 104a shown only in a circular portion represent a posture standing along a direction substantially perpendicular to the substrate surface, and the liquid crystal molecules in which the rod-like portion is shown longer. About 104a, it represents that it has fallen at a larger angle from the direction perpendicular to the substrate surface. The configuration conditions and process conditions other than the pixel electrode were the same as those in Example 1.

  In the comparative example, as shown in FIGS. 11A and 11B, in the liquid crystal layer 104, there is a difference in applied voltage between the region A immediately above the slit 102a1 and the region B directly above the electrode portion 102a2. (Electric field distortion is likely to occur). For this reason, in the region A, the liquid crystal molecules 104a are less likely to fall than in the region B. As a result, when the image is displayed, the transmitted light amount in the region A is smaller than that in the region B. Therefore, a locally low-luminance portion (dark line) is generated due to the slit position, and the transmittance is reduced. End up. In addition, since the luminance distribution is not uniform, the display image quality is deteriorated.

  On the other hand, in the present embodiment, the pixel electrode 12 has a two-layer electrode structure including a first sub electrode 12A having a plurality of slits 12a1 and a solidly formed second sub electrode 12B. A dielectric layer 13 is inserted between the sub electrode 12A and the second sub electrode 12B. Thereby, the voltage applied to the region A in the liquid crystal layer 15 and the voltage applied to the region B are set by appropriately setting the supply potential to each electrode of the counter electrode 17, the first sub electrode 12A, and the second sub electrode 12B. The magnitude relationship with the applied voltage can be freely controlled.

  Accordingly, when displaying an image, it is possible to drive so as to reduce the occurrence of electric field distortion in the entire liquid crystal layer 15. For this reason, in this Embodiment, it is suppressed that the transmittance | permeability falls, for example due to the pattern of slit 12a1.

(Setting of potential Va and Vb during video display)
Specifically, the potential Va supplied to the first sub-electrode 12A and the potential Vb supplied to the second sub-electrode 12B are reduced so that the difference between the voltages applied to the region A and the region B is reduced. Set. Note that here, for example, the case where the potential Va is a potential based on a video signal and the potential Vb is set according to the value of the potential Va will be described as an example, but conversely the potential Vb is a potential based on a video signal. Depending on this, the potential Va may be set.

The potential Vb is preferably set so as to satisfy the following expressions (1) and (2). Ideally, it is desirable to satisfy the following expression (3). By satisfying the expressions (1) and (2), a higher transmittance can be obtained than in the comparative example (FIG. 8) having the pixel electrode 102 having the single layer structure described above. Furthermore, since the voltages between the regions A and B can be made substantially equal by satisfying the expression (3), the electric field formed in the liquid crystal layer 15 becomes flat, and the pixel electrode 12 is substantially slit. It can be regarded as a solid electrode with no unevenness. Accordingly, the transmittance can be further increased, and the luminance distribution is made uniform, so that a good display image quality can be realized.
0.8 {Va × (C _INS + C _LC ) / C _INS } ≦ Vb (1)
Vb ≦ 1.2 {Va × (C _INS + C _LC ) / C _INS } (2)
Vb = Va × (C _INS + C _LC ) / C _INS (3)

Here, the derivation of the above formulas (1) and (2) will be described. 12 to 14 show the relationship between the potential Vb and the transmittance when the potential Va is 10 V (constant) as Example 2. FIG. The configuration conditions and process conditions for the pixel electrode 12, the liquid crystal layer 15, and the alignment films 14 and 16 were the same as in Example 1 above. However, the thickness T of the dielectric layer 13 was 200 nm in FIG. 12, 400 nm in FIG. 13, and 1000 nm in FIG. Further, the transmittance is described as the amount of emitted light / the amount of incident light, and the maximum transmittance is described as 1. Note that the transmittance in the comparative example (FIG. 10) having the pixel electrode 102 having the single-layer structure described above is 0.88 when a potential of 10 V (constant) is supplied to the pixel electrode 102 as shown by the dotted line in each figure. It became. When T = 200 nm, C _LC = 15.8 × 10 ⁻¹² F, C _INS = 267 × 10 ⁻¹² F, and when T = 400 nm, C _LC = 15.8 × 10 ⁻¹² F, C _INS When C = 134 × 10 ⁻¹² F and T = 1000 nm, C _LC = 15.8 × 10 ⁻¹² F and C _INS = 26.7 × 10 ⁻¹² F.

In Example 2, since the capacitance C _INS changes according to the thickness T of the dielectric layer 13, the transmittance characteristics with respect to the potential Vb are different. In any case, the transmission of the comparative example is different. It is desirable to achieve a transmittance that exceeds the rate (0.88). Table 1 shows an ideal potential (potential satisfying the above formula (3)) Vb0 and a potential at which the transmittance becomes 0.88 (in comparison with the comparative example) when the thickness T of the dielectric layer 13 is 200 nm, 400 nm, and 1000 nm. A potential Vb1 having an equivalent transmittance and a ratio thereof (Vb1 / Vb0) are shown.

As shown in Table 1, when the thickness T = 200 nm, the potential Vb0 is 10.6V and the potential Vb1 is 8.2V. When the thickness T = 400 nm, the potential Vb0 is 11.2V and the potential Vb1 is 8.9V. Thus, when the thickness T = 1000 nm, the potential Vb0 was 13.0V and the potential Vb1 was 9.6V. Vb1 / Vb0 was 0.77, 0.80, and 0.75, respectively, and the fluctuation range of the potential Vb1 with respect to the ideal potential Vb0 was 23%, 20%, and 25%, respectively. From these results, it can be seen that it is desirable to set the potential Vb so that the fluctuation range with respect to the ideal potential Vb0 is within 20% in order to achieve higher transmittance than the comparative example. That is, the potential Vb given by the above equation (3) is an ideal value, but if it is 0.8 times or more and 1.2 times or less (that is, the above equations (1) and (2) are satisfied). A higher transmittance than in the comparative example.

15A to 15D show examples of electric field distributions (equipotential distributions) formed in the liquid crystal layer 15 by the potentials Va and Vb satisfying the above expressions (1) and (2). Example 3) is shown. However, in each figure, X (μm) indicates a scale in a direction orthogonal to the extending direction of the slit 12a1 on the substrate surface. Z (μm) is a scale in the thickness direction of the liquid crystal layer 15, where Z = 0 is the first sub-electrode 12A side (alignment film 14 side), and Z = 3.5 μm is the counter electrode side (alignment film 16 side). To do. In the liquid crystal display panel 2, the configuration requirements and process conditions of the first sub-electrode 12A, the dielectric layer 13, the alignment films 14 and 16, and the liquid crystal layer 15 were the same as those in Example 1. Thereby, also in Example 3, it was set to _CLC = 15.8 * 10 < ^-12 > F and _CINS = 267 * 10 < ^-12 > F.

  For such a liquid crystal display panel 2, the potential Va was set to 10 V (constant), and a voltage was applied to the liquid crystal layer 15 while changing the potential Vb. Specifically, the ratio of the potential Vb to the potential Va (Vb / Va) was set to be 1, 1.05, 1.1, and 1.2, respectively. As shown in FIGS. 15A to 15D, by setting the potentials Va and Vb while satisfying the above expressions (1) and (2), the liquid crystal layer 15 has the electric field distribution ( Compared with FIG. 11A, it can be seen that the voltage difference between the regions A and B is reduced, and the electric field distortion is reduced. Thereby, generation | occurrence | production of the dark line resulting from the slit 12a1 is suppressed, and high transmittance | permeability is implement | achieved (FIG. 16 (A)-(D)). 16A to 16D are measurement results of the transmittance distribution on the XY plane in Example 3. FIG.

  Further, here, the case of Vb / Va = 1.05 (Vb = 10.5 V) shown in FIG. 15B is close to Vb = 10.6 V satisfying the above formula (3), which is almost ideal. It has an electric field distribution (flat electric field distribution). However, the combination of the potentials Va and Vb is not limited to this. The potential based on the video signal, the liquid crystal material and thickness of the liquid crystal layer 15, the monomer material, the scale of the slit 12a1 and the electrode portion 12a2 of the first sub-electrode 12A, the dielectric What is necessary is just to set suitably according to the material, thickness, etc. of the body layer 13. FIG.

Instead of the above formula (3), the potentials Va and Vb are equal to each other for the same reason as the case where the potentials Va and Vb are set so as to satisfy the formula (6) in the manufacturing process. Expression (4) may be satisfied.
Vb = Va (4)

  As described above, in the present embodiment, the pixel electrode 12 has a two-layer electrode structure of the first sub electrode 12A and the second sub electrode 12B, and the first sub electrode 12A and the second sub electrode. A dielectric layer 13 is provided between 12B. Therefore, by appropriately setting the potentials Va and Vb to be supplied to the first sub electrode 12A and the second sub electrode 12B, the applied voltage to the region A immediately above the slit in the liquid crystal layer 15 and the region B without the slit The magnitude relationship with the applied voltage can be freely controlled according to the purpose. For example, at the time of displaying an image, it is possible to perform driving so as to reduce the electric field distortion in the entire liquid crystal layer 15 by reducing the influence from the slit 12a1 as much as possible. As a result, for example, a local transmittance decrease due to the slit position Can be suppressed. On the other hand, in the manufacturing process (pretilt imparting step), the function of the slit 12a1 can be effectively exhibited, and an electric field distortion (lateral electric field) advantageous for imparting the pretilt can be generated. Therefore, it is possible to improve the transmittance while maintaining good voltage response characteristics.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to these embodiments and the like, and various modifications are possible. For example, in the above-described embodiment, the supply potential Va to the first sub-electrode 12A is set to 10V (constant), and the potential Vb is set based on this potential Va and any one of the above formulas (1) to (6). However, the potential Va is of course not limited to 10 V, and may be other values.

  Further, in the video display, the potential Va is described as the potential based on the video signal. However, the potential based on the video signal may be set as the potential Vb, or both of the potentials Va and Vb are set in the above (1) to An appropriate value may be set based on (4).

Furthermore, the material, thickness, dimensions, and the like of each layer in the liquid crystal display device of the present invention are not limited to those described above. For example, for the liquid crystal layer 15 and the dielectric layer 13, the capacitances C _LC and C _INS between the electrodes vary depending on the method of selecting the material, thickness, etc., but the above formulas (1) to (6) The potentials Va and Vb may be set based on one of the above. In the first sub-electrode 12A, the case where the slit width S and the electrode portion width L are equal to each other (S = L = 4 μm) has been described as an example. However, the slit width S and the electrode portion The width L may be different from each other.

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... Liquid crystal display panel, 3 ... Backlight, 10 ... Pixel, 11 ... Drive board, 12 ... Pixel electrode, 12A ... 1st sub electrode, 12a1 ... Slit, 12a2 ... Electrode part, 12B ... 1st 2 sub-electrodes, 13 ... dielectric layer, 14, 16 ... alignment film, 15 ... liquid crystal layer, 15a ... liquid crystal molecule, 17 ... counter electrode, 18 ... counter substrate, 19 ... incident side polarizing plate, 20 ... outgoing side polarizing plate , 51 ... Data driver, 52 ... Gate driver, 61 ... Timing controller, 62 ... Backlight drive unit, Va, Vb ... Potential, C _LC , C _INS ... Capacitance, θ ... Pretilt angle, D1 ... Long axis direction (Director).

Claims (14)

A liquid crystal layer;
A pair of substrates disposed opposite to each other with the liquid crystal layer interposed therebetween;
A plurality of pixel electrodes provided on the liquid crystal layer side of one of the pair of substrates;
A counter electrode provided on the other substrate facing the plurality of pixel electrodes,
Each pixel electrode includes, in order from the liquid crystal layer side, a first sub-electrode having one or a plurality of slits, a dielectric layer, and a second sub-electrode disposed at least in a region facing the slits. A liquid crystal display device. A drive unit for supplying a potential to each pixel electrode and the counter electrode;
The liquid crystal layer is applied with a voltage according to a potential difference between the first sub electrode and the counter electrode, a first region to which a voltage according to a potential difference between the first sub electrode and the counter electrode is applied, and a potential difference between the second sub electrode and the counter electrode. A second region to be
The driving unit applies each of the counter electrode and the first and second sub-electrodes so that a difference between voltages applied to the first region and the second region of the liquid crystal layer is reduced. The liquid crystal display device according to claim 1, wherein electric potential is supplied. The liquid crystal display device according to claim 2, wherein the driving unit supplies a potential so as to satisfy the following expressions (1) and (2).
0.8 {Va × (C _INS + C _LC ) / C _INS } <Vb (1)
Vb <1.2 {Va × (C _INS + C _LC ) / C _INS } (2)
However,
Va: potential difference between the first sub-electrode and the counter electrode Vb: potential difference between the second sub-electrode and the counter electrode C _INS : capacitance C _LC between the first and second sub-electrodes: first The capacitance between one sub-electrode and the counter electrode. Furthermore, the liquid crystal display device of Claim 3 which satisfies the following formula | equation (3).
Vb = Va × (C _INS + C _LC ) / C _INS (3) Furthermore, the liquid crystal display device of Claim 3 which satisfies the following formula | equation (4).
Vb = Va (4) The liquid crystal display device according to claim 1, wherein in each pixel electrode, the first sub-electrode has a plurality of slits. The liquid crystal display device according to claim 6, wherein the second sub electrode is provided over the entire area of the first sub electrode. The liquid crystal display device according to claim 1, wherein a pretilt is applied in the vicinity of the pixel electrode and the counter electrode in the liquid crystal layer. Forming a plurality of pixel electrodes on one of the pair of substrates;
Forming a counter electrode on the other substrate;
Sealing a liquid crystal layer between the pair of substrates;
Applying a pre-tilt to the liquid crystal layer by exposing the liquid crystal layer while applying a voltage to the liquid crystal layer through the pixel electrode and the counter electrode,
In the step of forming the plurality of pixel electrodes,
As each pixel electrode, a second sub-electrode, a dielectric layer, and a first sub-electrode having one or a plurality of slits are formed in this order so as to face the second sub-electrode from the one substrate side. A method for manufacturing a liquid crystal display device. The liquid crystal layer is applied with a voltage according to a potential difference between the first sub electrode and the counter electrode, a first region to which a voltage according to the potential difference between the first sub electrode and the counter electrode is applied, and a potential difference between the second sub electrode and the counter electrode. A second region to be
The method for manufacturing a liquid crystal display device according to claim 9, wherein in the step of applying the pretilt, different voltages are applied to the first region and the second region of the liquid crystal layer. The method for manufacturing a liquid crystal display device according to claim 10, wherein a voltage is applied to the liquid crystal layer so as to satisfy the following expression (5).
Vb ≠ Va × (C _INS + C _LC ) / C _INS (5)
However,
Va: potential difference between the first sub-electrode and the counter electrode Vb: potential difference between the second sub-electrode and the counter electrode C _INS : capacitance C _LC between the first and second sub-electrodes: first The capacitance between one sub-electrode and the counter electrode. Furthermore, the manufacturing method of the liquid crystal display device of Claim 11 which satisfies the following formula | equation (6).
Vb = Va (6) In the step of forming the plurality of pixel electrodes,
The method for manufacturing a liquid crystal display device according to claim 9, wherein a plurality of slits are formed in the first sub-electrode. The method for manufacturing a liquid crystal display device according to claim 13, wherein the second sub-electrode is formed over the entire area of the first sub-electrode.

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